Raspberry Pi 400 will not power down

Running Tumbleweed on a Pi 400 (booted from SD) with XFCE DE, and it’s all good, except one thing I can’t figure out.

When I try to power down, the system goes through the usual motions, but once the OS has finished, rather than physically powering off, as every other system I’ve run on this machine does 100% fine, this one decides to restart without powering down, as if I had done ‘restart’ not ‘power down’. Does this over and over, every time I try to power down.

I put the SD card into my Pi 4 machine, booted up, then powered down, it works fine, system powers down as it should. The Pi 400 also powers down when told to, when running Pi OS booted from a USB drive. It is just the openSUSE system that the Pi 400 restarts instead of powering down. Tried powering down as root rather than my usual login, same issue.

Anyone seen this, and if so, could you please direct me towards what needs doing to get it to behave?

Many thanks